EUVD-2026-12425
GHSA-xpvf-6qcc-9jqc
Severity by source
AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
Primary rating from NVD.
CVSS VectorNVD
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
Lifecycle Timeline
4DescriptionCVE.org
Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to validate team-specific upload_file permissions which allows a guest user to post files in channels where they lack upload_file permission via uploading files in a team where they have permission and reusing the file metadata in a POST request to a different team. Mattermost Advisory ID: MMSA-2025-00553
AnalysisAI
This vulnerability in Mattermost allows guest users to bypass team-specific file upload permissions through a cross-team file metadata reuse attack. Affected versions include Mattermost 11.3.0, 11.2.x up to 11.2.2, and 10.11.x up to 10.11.10. An authenticated guest user can upload a file in a team where they have upload_file permission, then reuse that file's metadata in POST requests to channels in different teams where they lack upload permission, resulting in unauthorized file posting with potential integrity impact.
Technical ContextAI
The vulnerability stems from inadequate permission validation at the application layer in Mattermost's file upload handling mechanism. Mattermost (identified via CPE as cpe:2.3:a:mattermost:mattermost) implements role-based access control with team-scoped and channel-scoped permissions, including the upload_file capability. The root cause falls under CWE-863 (Incorrect Authorization), specifically a failure to re-validate permission context when file metadata is referenced across team boundaries. The application accepts file metadata identifiers in POST requests without re-confirming that the requesting user has upload_file permission within the target team's context, allowing permission context to be bypassed by reusing previously-authorized file references.
RemediationAI
Upgrade Mattermost to version 11.3.1 or later (11.3.x series), 11.2.3 or later (11.2.x series), or 10.11.11 or later (10.11.x series) as specified in Mattermost Advisory MMSA-2025-00553. Organizations unable to patch immediately should restrict guest user provisioning where possible, enforce uniform upload_file permissions across all teams for guest accounts to eliminate permission variance exploitation, and implement application-level logging and alerting on cross-team file metadata references. Review file upload audit logs to detect potential exploitation of this vulnerability prior to patching.
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Same weakness CWE-863 – Incorrect Authorization
View allSame technique Authentication Bypass
View allVendor StatusVendor
SUSE
Severity: Medium| Product | Status |
|---|---|
| openSUSE Leap 15.6 | Fixed |
| SUSE Linux Enterprise Module for Package Hub 15 SP5 | Fixed |
| SUSE Linux Enterprise Module for Package Hub 15 SP6 | Fixed |
| openSUSE Leap 15.5 | Fixed |
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External POC / Exploit Code
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